J. Guilera et al. / Reactive & Functional Polymers 78 (2014) 14–22
15
Nomenclature
DCE
DEC
DEE
DNOE
DOC
dp
dpore
EOC
EOE
EtOH
ISEC
nj
1,2-dichloroethane
diethyl carbonate
diethyl ether
ROcOH/EtOH OcOH/EtOH initial molar ratio (mol/mol)
S-DVB
SBET
Sjk
TOF
TOFrel
Vi
V0
Vsp
W
styrene-co-divinylbenzene
BET surface area (m2/g)
di-n-octyl ether
dioctyl carbonate
particle diameter (
selectivity to k with respect to j (%, mol/mol)
initial turnover frequency (mol/h mol H+)
relative turnover frequency (ꢀ)
resin volume in water (cm3)
l
m)
pore diameter (nm)
ethyl octyl carbonate
ethyl octyl ether
resin volume in air (cm3)
specific volume of the swollen polymer (cm3/g)
dry catalyst mass (g)
ethanol
inverse steric exclusion chromatography
moles of EOE or EOC, mol
1-octanol
Xj
conversion of j (%, mol/mol)
[H+]
acid capacity (mmol H+/g)
OcOH
ROcOH/DEC OcOH/DEC initial molar ratio (mol/mol)
such partially functionalized resins for esterification process,
favoring in this way the formation of esters over that of ethers
[18]. Eventually, the partially sulfonated macroreticular resin
Amberlyst 46 (hereinafter called surface sulfonated) was commer-
cialized [19]. Specific acid site distribution in Amberlyst 46 has
been used nowadays to study the influence of the acid sites loca-
tion on many reaction processes, as well, to optimize the selectivity
to the desired products [20–26].
In previous works, a relationship between the resin crosslinking
degree and the EOE yield was found [6,12,26]. In the present work,
the influence of the resin functionalization degree on EOE forma-
tion is studied. The performance of a series of partially sulfonated
resins was tested over two reaction pathways for obtaining EOE:
the dehydration reaction between OcOH and EtOH; and the transe-
sterification reaction between OcOH and DEC to form ethyl octyl
carbonate, and its subsequent decomposition to EOE.
concentrated sulfuric acid and afterwards, the mixture was stirred
and heated for 6 h at a temperature selected to achieve the desired
degree of sulfonation (T = 30–80 °C). The sulfonation reaction time
and temperature (to control the conversion) were selected with the
aim of limiting differences in the sulfonation degree at the periph-
ery and center of the polymer beads. Then, the mixture was slowly
cooled down and diluted by percolation with sulfuric acid solution
of gradually diminishing concentration (90, 70, 50, 30 and 10 v/v%).
Eventually, the product was washed with deionised water untill
neutral pH of the eluent. Additionally, a fully sulfonated resin
was prepared by sulfonation of the polymer pre-swollen in DCE
overnight (50 mL) for 6 h at 80 °C.
2.3. Resin characterization
2.3.1. Swelling in water
The particle size distribution of the catalysts was determined by
means of a Laser Diffraction Particle Size Analyzer (LS 13320) in air
and immersed in water. Previously, samples were dried first at
110 °C at 1 bar and later at 110 °C under vacuum overnight. Then
they were placed in water for 2 days to assure that resins were
completely swollen [11]. Resin swelling degree was calculated as
the relative volume increase with respect to resin volume in air
flow by Eq. (1), where Vi is the mean particle volume in water,
and Vo is the volume of dry resin in air. Volumes were calculated
under the assumption that particles are spherical.
2. Experimental
2.1. Materials
OcOH (P99%, Acros), DEC (P98%, Fluka) and EtOH (P99.8%,
Panreac) were used as reactants in catalytic tests. DEE (P99%, Pan-
reac), di-n-octyl ether (DNOE) (P97%, Fluka) and EOE, produced
and purified in our lab, were used for analysis purposes. The mac-
roreticular styrene-co-divinylbenzene (S-DVB) polymer (Spolche-
mie, Czech Republic) was the polymer base in resin catalysts
synthesis. Sulfuric acid (P95%, Lachner) and 1,2-dichloroethane
(DCE) (P99.8%, Acros) were used in resin sulfonation process.
The macroreticular acidic resins Amberlyst 15 and 46 (Rohm
and Haas) were used as catalysts for comparison purposes. Their
main characteristics are shown in Table 1. Both resins are based
on S-DVB copolymer with high content of DVB. Amberlyst 15
was selected as a fully monosulfonated macroreticular resin, which
statistically means, one sulfonic group per styrene ring; whereas
Amberlyst 46 was selected as a low sulfonated macroreticular
resin.
ꢀ
ꢁ
Vi
V0
fSwelling degreeg ¼
ꢀ 1 ꢁ 100 ½%ꢂ
ð1Þ
2.3.2. Swollen-state morphology
The inverse steric exclusion chromatography (ISEC) apparatus
consisted of HPLC pump (Waters 510), sampling valve, stainless
steel column (4.27 cm3) and refractometric detector (Shodex RI-
100). The detector signal was connected to a computer and the
sampling data was synchronized with the mobile phase flow rate
using a drop counter.
Catalysts
were
crushed,
sieved
in
swollen
state
2.2. Sulfonation procedure
(0.250 > dp > 0.125 mm) and placed overnight in the mobile phase
(0.2 N Na2SO4). Then, the swollen catalyst was packed in the col-
umn by flowing the mobile phase for 30 min (ꢃ5 mL/min). Later
on, the filled column was connected to the apparatus. During the
chromatographic measurements the standard solutes (deuterium
oxide, sugars and dextranes) were injected independently
A series of partially sulfonated resins were prepared from a
macroreticular S-DVB copolymer (DVB content about 20%). This
copolymer was originally manufactured as an intermediate for
production of ion exchanger Ostion KSPC (Spolchemie, Ústí nad La-
bem, Czech Republic). In order to achieve low-to-medium sulfona-
tion degrees, 15 g of the polymer was placed in 100 mL of
(20
lL). Elution volumes were determined on the basis of the first
statistical moments of the chromatographic peaks. For each